The invention relates generally to temperature sensing and compensating devices and, more particularly, to devices for sensing ambient or operating temperature of a motor vehicle transfer case or similar device and adjusting or compensating shifts or operating cycles in response to such sensed temperature.
In motor vehicle driveline components such as transmissions and transfer cases, operation over an extraordinarily wide range of both ambient and operating temperatures is acknowledged to occur. For example, starting and operation of vehicles at temperatures as low as xe2x88x9225xc2x0 F. (xe2x88x9232xc2x0 C.) and up to of 120xc2x0 F. (49xc2x0 C.) is a routine event of motor vehicle usage. Actual operating temperatures of components such as transmissions and transfer cases varies over an even wider temperature range inasmuch as such low temperatures will be achieved when the vehicle is started but operating temperatures will typically be 100xc2x0 to 125xc2x0 F. (55xc2x0 to 70xc2x0 C.) above ambient and thus such upper limits may well be 220 to 245xc2x0 F. (104xc2x0 to 118xc2x0 C.) and higher.
Coupled with such known and acknowledged ambient and operating temperature ranges is the temperature related viscosity of virtually all lubricants. The resistance to motion of a lubricating fluid in a shift mechanism at xe2x88x9225xc2x0 F. (xe2x88x9232xc2x0 C.), for example, requires significantly greater effort and thus actuator power than at much higher temperatures. Even with a more powerful actuator, a mechanical system operating at such low temperatures will invariably require more time to achieve a given mechanical action relative to the time taken by the same device at an elevated, operating temperature. In order to ensure that a desired action such as a shift from high to low gear or a shift into or out of four wheel drive has safely occurred, the control device may have to assume a worst case scenario: cold weather and allow a completion time which is excessively long in all but the coldest conditions. Such an operating scheme artificially delays shift completion in, for example, warm weather and is undesirable.
The increasing sophistication of transmission and transfer case control systems, the increasing demands of engineering sophistication and consumer sensitivity to noise, vibration and harshness (NVH) has prompted continuing examination of transmission and transfer cases in order to constantly re-evaluate and improve both the mechanical and electronic components and their performance. The present invention is directed to such an improvement.
A transfer case for a four-wheel drive motor vehicle includes an electronic control unit (ECU) and a synchronizer which facilitates shift on the fly operations such as, for example, a shift from two wheel high to four wheel high. A temperature sensor disposed either in the transfer case or elsewhere in the motor vehicle provides a temperature signal to the ECU which is utilized to adjust the on time of the synchronizer to compensate for the viscosity of the lubricating fluid within the transfer case and other temperature related variables which affect the time required to synchronize the drive line components prior to engagement. Such temperature compensation also facilitates fault detection and system oversight since the ECU can accurately anticipate the variability of the operating parameters based upon temperature and determine malfunctions when operation occurs outside such temperature-adjusted parameters.
It is thus an object of the present invention to provide a motor vehicle transfer case having a temperature compensated controller for a shift synchronizer.
It is a further object of the present invention to provide a motor vehicle transfer case having a temperature compensated controller for a shift mechanism synchronizer.
It is a still further object of the present invention to provide a motor vehicle transfer case having a temperature compensated controller for a shift on the fly synchronizer.
It is a still further object of the present invention to provide a motor vehicle transfer case having an electronic control unit with a temperature input for adjusting the synchronization period of a synchronized clutch to facilitate on the fly shifts.
Further objects and advantages of the present invention will become apparent by reference to the following description of the preferred embodiment and appended drawings wherein like reference numbers refer to the same component, element or feature.